The measurement of individual atomic mean-square displacements in proteins by X-ray crystallography will be carried out to map the spatial distribution of protein internal motions. The temperature and pressure of the crystals will be varied to understand the thermodynamics of the fluctuations. The influence of ligand binding on the different fuctuations will be probed by doing the analysis on complexes as well as native proteins. Comparisons will be made with displacement values measured by other techniques, and with those calculated from molecular dynamics simulations. Where possible, anisotropic temperature factors will be fit to the date to give the principal directions as well as the amplitudes of motion.